This invention relates to methods for making cylinder heads for internal combustion engines with intake or exhaust port liners.
Port liners are used in internal combustion engines to provide heat insulation between the hot exhaust gases and the cylinder head. For the same reason, such liners are usually included in the exhaust and intake passages as well. European Patent Application No. 0 339 453 discloses a tubular insert, for example, a pressed hollow sheet metal fitting in the cylinder head, for the purpose of achieving especially favorable flow conditions in a compression change gas passage. In that disclosure, the gas passage is fabricated using removable cores, which do not permit free forming of the passage.
According to the European application, the port liner is inserted into a passage which is produced by the removable cores after the cylinder head has been formed by injection or pressure casting. On the other hand, the port liners disclosed in German Offenlegungsschrift No. 26 02 434 and German Patent No. 29 48 910 provide a core or lost mold to shape the compression change passage during casting of the cylinder head. However, a disadvantage of both of these known methods is that the valve seat ring and the valve guide associated with the passage must either be positioned in the mold as separate parts during casting or subsequently mounted in the cylinder head after casting.
Understandably, however, the latter two constructions, in which the port liner is cast in, are advantageous in comparison to the manufacture of the cylinder head compared to the arrangement disclosed in German Offenlegungsschrift No. 23 23 793. According to that disclosure, the port liner is inserted after the casting operation and is connected to the valve seat ring by welding or by a pin connection, for example. Moreover, that arrangement requires an opening in the port liner in the vicinity of the valve guide, which must pass through a recess in the port liner in gas-tight relation to the liner.
Finally, German Offenlegungsschrift No. 25 37 676 discloses a heat-insulating liner for the exhaust passage of an internal combustion engine in which the liner also forms the valve seat ring and is cast into the cylinder head. The exhaust passage has a lift valve with a valve seat ring traversing a recess in the port liner and projecting comparatively far into the flow passage.